The present invention relates to an apparatus and method for detecting a damaged aerofoil, in particular for detecting a damaged gas turbine engine fan blade, a gas turbine engine compressor blade, a gas turbine engine turbine blade, a gas turbine engine fan outlet guide vane, a gas turbine engine compressor vane or a gas turbine engine turbine vane.
Gas turbine engines, particularly on aircraft, are susceptible to objects entering the gas turbine engine. These objects may be relatively soft objects, for example birds, or relatively hard objects, for example stones. The majority of hard objects entering a gas turbine engine are relatively small and produce localised damage to the gas turbine engine blades, for example relatively small dents or nicks. Some of the soft objects entering the gas turbine engine frequently produce no damage to the gas turbine engine blades. However, some relatively large soft objects, for example birds, entering the gas turbine engine produce widespread damage to the gas turbine engine blades.
Gas turbine engine blades may also suffer damage, on very rare occasions, by colliding with other blades or vanes in an adjacent row of blades or an adjacent row of vanes. The collision with other blades, or vanes, may result in widespread damage to the gas turbine engine blades or gas turbine engine vanes.
It is highly desirable to detect widespread damage to a gas turbine engine blade or a gas turbine engine vane before it causes failures.
Gas turbine engine blades are periodically inspected for damage. If a damaged gas turbine engine blade is detected it is replaced, or repaired, as required. In the case of gas turbine engines provided on aircraft, the gas turbine engines are visually inspected prior to each flight. However, these pre-flight inspections often take place under difficult circumstances and damaged gas turbine engine blades may not always be detected by the pre-flight inspection.
Accordingly the present invention seeks to provide a novel apparatus and method for detecting widespread damage to one or more aerofoils of a set of aerofoils which may not have been detected by pre-use inspection.
Accordingly the present invention seeks to provide a novel apparatus and method for detecting widespread damage to one or more aerofoils of a set of aerofoils while the aerofoils are in operation.
Accordingly the present invention provides a rotary machine comprising a plurality of aerofoils arranged in a set, an apparatus for detecting damage to at least one of the aerofoils in the set, the apparatus for detecting damage to at least one of the aerofoils in the set comprising at least one pressure transducer arranged to detect the pressure in the fluid flow around the aerofoils in the set and to produce a pressure signal corresponding to said pressure, a processor unit arranged to analyse the pressure signal to determine if the difference in pressure between the fluid flow around at least one of the aerofoils in the set and the fluid flow around the remainder of the aerofoils in the set is above a predetermined level, the processor unit is arranged to produce a signal indicative of damage to at least one of the aerofoils in the set if the difference in pressure is above the predetermined level and to send the signal to an indicator device.
Preferably the machine comprises a rotor and a stator, the aerofoils are rotor blades mounted on the rotor and the at least one pressure transducer is mounted on the stator.
Alternatively the machine comprises a rotor and a stator, the aerofoils may be stator vanes mounted on the stator and the at least one pressure transducer is mounted on the rotor.
The rotor blades may be gas turbine engine fan blades or gas turbine engine compressor blades.
The stator vanes may be gas turbine engine fan outlet guide vanes or gas turbine engine compressor vanes.
Preferably a speed sensor is arranged to detect the speed of rotation of the rotor and to produce a speed signal corresponding to said speed, the processor unit being arranged to analyse the speed signal to determine the rotational frequency of the rotor, the processor unit being arranged to analyse the pressure signals and the rotational frequency of the rotor to detect changes in the amplitude of the pressure which occur at the same frequency as, or at multiples of the rotational frequency of, the rotational frequency of the rotor.
The pressure transducer may have a low pass mechanical sensitivity to detect low frequency fluctuations in pressure.
Alternatively a low pass electrical filter may be arranged to filter the pressure signal before it is analysed by the processor unit.
Alternatively a low pass acoustic filter may be arranged to filter the pressure in the gas flow around the All blades before it is detected by the pressure transducer.
Alternatively the processor unit may have means to sample the pressure signal at high frequency and means to perform a Fourier transformation.
The at least one pressure transducer may be arranged upstream of the aerofoils or downstream of the aerofoils.
Preferably a casing is arranged around the rotor blades and the casing partially defines a duct in which the rotor blades rotate.
Preferably the at least one pressure transducer is arranged in the casing.
Alternatively the at least one pressure transducer is arranged in the duct.
The present invention also provides a method of detecting damage to a rotary machine aerofoil, the machine comprising a plurality of aerofoils arranged in a set, the method comprising detecting the pressure in the fluid flow around the aerofoils in the set and producing a pressure signal corresponding to said pressure, analysing the pressure signal to determine if the difference in pressure between the fluid flow around at least one of the aerofoils in the set and the gas flow around the remainder of the aerofoils in the set is above a predetermined level, producing a signal indicative of damage to at least one of the aerofoils in the set if the difference in pressure is above the predetermined level and sending the signal to an indicator device.
Preferably the machine comprises a rotor and a stator, the aerofoils are rotor blades mounted on the rotor and the at least one pressure transducer is mounted on the stator.
Alternatively the machine comprises a rotor and a stator, the aerofoils may be stator vanes mounted on the stator and the at least one pressure transducer is mounted on the rotor.
Preferably the rotor blades are gas turbine engine fan blades or gas turbine engine compressor blades, the method comprising detecting the pressure in the fluid flow around the fan blades or detecting the pressure in the fluid flow around the compressor blades.
Alternatively the stator vanes are gas turbine engine fan outlet guide vanes or gas turbine engine compressor vanes, the method comprising detecting the pressure in the fluid flow around the fan outlet guide vanes or detecting the pressure in the fluid flow around the compressor vanes.
Preferably the method comprises measuring the speed of rotation of the rotor, analysing the speed of rotation of the rotor to determine the rotational frequency of the rotor, analysing the pressure signals and the rotational frequency to detect changes in the amplitude of the pressure which occur at the same frequency as, or at multiples of the rotational frequency of, the rotational frequency of the rotor.
The method may comprise detecting low frequency fluctuations in pressure.
Alternatively the method may comprise filtering the pressure signal before it is analysed using a low pass electrical filter.
Alternatively the method may comprise filtering the pressure in the gas flow around the rotor blades before it is detected using a low pass acoustic filter.
Alternatively the method may comprise sampling the pressure signal at high frequency and performing a Fourier transformation.
The method may comprise detecting the pressure upstream of the aerofoils or downstream of the aerofoils.
Preferably a casing is arranged around the rotor blades and the casing partially defines a duct in which the rotor blades rotate.
Preferably the method comprises detecting the pressure Fusing at least one pressure transducer arranged in the casing.
Alternatively the method comprises detecting the pressure using at least one pressure transducer arranged in the duct.